Electric bicycle and methods

ABSTRACT

An electric motor assembly comprises a housing and a spindle disposed to rotate in the housing. A motor is provided which comprises a stator coupled to the housing, and a rotor rotatably disposed within the stator such that the rotor is disposed about the spindle. The assembly further includes an output driver, and a gear system operably coupled to the rotor and the output driver to rotate the output driver upon operation of the motor.

BACKGROUND OF THE INVENTION

The invention relates generally to the field of cycles, and inparticular to bicycles. More specifically, the invention relates to anelectric assist bicycle which is configured to maximize the efficiencyof the motor and to prolong the life of the battery which supplieselectrical current to the motor.

Over the last 150 years, the bicycle has evolved to become one of themost efficient means of transportation in terms of conversion of energyinto distance travelled. For example, most modern bicycles require onlyabout 400 watts (½ horsepower) to propel the bicycle at 15 m.p.h. onlevel ground. The efficiency of the bicycle has also been optimized tominimize the effort required by the rider. For instance, most modernbicycles include an efficient gear system to minimize rider effort.

To further reduce the amount of human effort required to propel abicycle, a variety of electric bicycles have been introduced. Presently,about 50 to 100 companies are producing or are planning to produceelectric bicycles. In most cases, however, such bicycles do not utilizethe efficiency of the bicycle through the use of mechanical gears.

The human muscle and modern battery are similar in their ability toproduce power from stored energy. Similarly, both are able to producemore energy by keeping the torque per stroke low and the frequency high.

The human muscle is able to function in two states: anaerobic oraerobic. In anaerobic contraction, the muscle utilizes stored ATP fuelto power the muscle without the need for oxygen. In this case, themuscle can produce large amounts of energy for a short duration. Thebyproduct of this high energy output is lactic acid. As musclecontraction continues in an anaerobic state, the lactic acid in themuscle builds until it inhibits further muscle contraction. After aperiod of rest, the lactic acid is removed from the muscle by the bloodsystem and muscle contraction can continue (assuming a sufficient storeof ATP fuel). Aerobic muscle contraction allows for extended periods ofexertion, but at a lower level of power than anaerobic exercise. Inaerobic exercise, sufficient oxygen is supplied to the muscle so thatthe muscle is able to use the soluble fat in the blood as the primaryfuel.

The gears of modern bicycle allow the rider to exercise the muscle inthe aerobic range to allow continuous long distance riding. The gearsare utilized to keep the rider's pedal speed at a high rotating speed(usually between about 60 to 100 rpm). At higher pedaling speeds, theforce output for muscle contraction is low so that the muscle is able tostay in the aerobic region.

The original bicycle used a single fixed gear ratio (similar to mostelectric bicycles) and was severely limited in its ability to negotiatesteep terrain. The number of gears on a bicycle has evolved so that thepresent mountain bike has up to 27 gears to allow for riding on avariety of terrains.

Similar to the human muscle, the modern battery has an efficient and aninefficient region. The battery delivers current to the motor, whichproduces torque in the motor. The motor torque increases linearly withmotor current. High currents are inefficient.

At high current discharge rates, the battery experiences problemssimilar to lactic acid buildup in the human muscle. More specifically,in the battery, hydrogen gas is formed on the charge plate. Hydrogen gasacts as a barrier to the transfer of electrons. As the high currentdischarge continues, the hydrogen continues to build on the plates untilthe battery is unable to deliver current.

Another important issue to consider at high current discharge rate isthat the run time of the battery is reduced exponentially with linearincreases in motor current. Further, motor thermal losses areexperienced which increase with the square of the motor current. Hence,increased motor current wastes available energy two non-linear ways,i.e., battery losses and motor resistance losses.

As one example, a motor mounted directly to the rear wheel on thebicycle has only a fixed gear ratio. Hence, to obtain a four timesincrease in torque, the motor current must be increased by four times.However, the four times increase in the motor current increases motorresistive losses by 16 times and thus results in a significant loss inbattery run time and reduction in motor efficiency.

The available power from the battery is an exponential function of therate of current use. Hence, as current discharge increases, theavailable energy from the battery decreases exponentially. Hence, asmore torque is required to move the bicycle (such as during hillclimbing or acceleration), more current will be required, therebyexponentially decreasing the available power from the battery.

Hence, it would be desirable to provide improved electrically assistedbicycles and methods for their use which would overcome or greatlyreduce these and other problems. The electric bicycles of the inventionshould be configured to maximize the efficiency of the motor, minimizecurrent use, and thus maximize battery life. It would be desirable ifsuch features could be accomplished by minimizing the required torquewhile keeping the rotational rate of the motor as high as possible.Preferably, the electric bicycles of the invention will employ the useof a gear system so that torque may be minimized, especially during hillclimbing and acceleration. It would further be desirable if the electricbicycles of the invention provided for automatic shifting to keep themotor speed near maximum output while minimizing torque. In anotheraspect, it would be desirable if such electric bicycles were able tooperate using either the motor or the pedals in a parallel manner. Atthe same time, it would be preferable if such electric bicycles employedthe use of a motor which did not turn the crank arms. Such electricbicycles and methods should also be compatible with conventional bicycleequipment, such as derailleurs so that shifting may be accomplished withminimal modification to existing bicycles. Finally, it would bepreferable to incorporate the batteries into the bicycle in a mannersuch that the overall appearance of the bicycle is aestheticallypleasing, such the batteries are protected, and such that the bicycle isprovided with a low center of gravity.

SUMMARY OF THE INVENTION

The invention provides exemplary electric motor assemblies, electricallyassisted bicycles, and methods for their use. In one exemplaryembodiment, the invention provides an electric motor assembly whichcomprises a housing and a spindle that is disposed to rotate in thehousing. A motor is disposed within the housing and comprises a statorcoupled to the housing and a rotor rotatably disposed within the statorsuch that the rotor is disposed about the spindle. The motor assemblyfurther includes an output driver, and a gear system operably coupled tothe rotor and the output driver to rotate the output driver uponoperation of the motor.

The disposition of the motor and output driver within the housing isadvantageous in that it facilitates packaging and manufacturing of themotor assembly. Preferably, the spindle is aligned with a central axisof the housing, with the rotor being concentrically disposed about thespindle, and the stator being concentrically disposed about the rotor.Such a configuration allows for a compact design to allow the motor toconveniently fit within the housing.

In another particularly preferable aspect, a front sprocket assembly isoperably coupled to the output driver such that the sprocket assemblyrotates upon rotation of the output driver. By having the motor turn thesprocket assembly, the motor assembly may be used in connection withmechanical gears of the modern bicycle to minimize the amount of torquerequired, thereby greatly increasing battery life.

In another particular aspect, the gear system is coupled to a motordriver. The motor assembly further includes a first clutch to engage themotor driver with the output driver when the motor driver is rotatedfaster than the output driver. In this way, when the rider is pedalingat a rate which causes the output driver to rotate faster than the motoris turning the motor driver, the first clutch will not engage the motordriver with the output driver. Hence, the rider is able to pedal thebicycle and not turn the motor. Conversely, if the motor turns the motordriver at a rate which is faster than the rider is pedalling, the firstclutch is engaged so that the motor causes the output driver (and hencethe sprockets) to rotate. Optionally, another clutch mechanism may beprovided which allows the rider to engage the clutch during pedaling forregenerative charging of the battery.

In yet another aspect, a crank arm is coupled to the spindle, and apedal is coupled to a crank arm. A second clutch is also provided toengage the crank arm with the output driver when the crank arm isrotated faster than the output driver (thereby releasing the firstclutch) so that the rider's legs cause rotation of the output driver.Use of the second clutch is also advantageous because, when the motor isturning the output driver, the second clutch will ensure that the crankarm is disengaged. In this way, the motor is able to turn the sprocketassembly but not the crank arms. Preferably, the first clutch and thesecond clutch are coaxially aligned with an axis of the spindle to allowfor packaging of the motor in the small space available between thecrank arms.

In yet another aspect, the gear system comprises a set of planetarygears to rotate the output driver at a rate of rotation that is lessthan the motor. Preferably, the gears are configured so that the outputspeed of the motor is matched to the range of the human leg. Forexample, the planetary gears are preferably configured so that when therate of rotation of the motor is in the rate from about 1,800 rpm toabout 3,600 rpm, the rate of rotation of the output driver is in therange from about 60 rpm to about 120 rpm. In a specific aspect, themotor speed is approximately 2400 rpm and is employed to turn the crankarms at a rate of about 75 rpm. Such a gear reduction facilitates use ofeither the motor or pedal power to drive the bicycle. The motor ispreferably operated at or near its maximum output level to maximize theefficiency of the motor and minimize current use, thereby prolonging thelife of the battery. Operating the motor at or near its maximum outputlevel is also advantageous in that the motor is able to generate morepower at higher rates of rotation.

In still yet another aspect, the motor comprises a brushless DC motor.Such a motor is preferable because it provides superior cooling and ahigh power output. Alternatively, a brushed or SR motor may be used.

In one particular aspect, at least one bearing assembly is coupled tothe housing and disposed about the spindle. In this way, the pedals arefree to turn when operated by a rider. Use of the bearing assembly isalso advantageous in that the crank spindle is used to support the rotorand the planetary gears. Another bearing assembly is preferably disposedbetween the rotor and the spindle so that rotation of the rotor isgenerally prevented upon rotation of the spindle by the crank arm. Inthis way, the rider may pedal the bicycle without turning the motor.Also, this bearing assembly prevents the spindle, and therefore thecrank arms, from rotating when the motor is operating.

The invention further provides an exemplary cycle which comprises aframe having a bottom bracket. At least one wheel is operably coupled tothe frame. The bicycle further includes a motor assembly that isdisposed within the bottom bracket. Preferably, the motor assembly isconstructed to be similar to the motor assembly just described. A firstsprocket assembly is coupled to the output driver of the motor assemblysuch that the sprocket assembly rotates upon rotation of the outputdriver. A second sprocket assembly is coupled to the wheel, and a chainis coupled between the first sprocket assembly and the second sprocketassembly to rotate the wheel upon rotation of the output driver.

The disposition of the motor assembly in the bottom bracket isparticularly advantageous in that the motor is housed at a low center ofmass of the cycle. Advantageously, the motor is not disposed on thewheel which may otherwise add unsprung mass and cause poor suspensionand handling and added rotational dynamics. By packaging the motor inthe bottoming bracket, the motor is extremely efficient.

In one particularly preferable aspect, the frame defines a cavity, andat least one battery is housed within the cavity and is electricallycoupled to the motor. Preferably, the bicycle frame is constructed of amonocoque design having a hollow center for receiving the battery. Inthis way, the battery may be mounted in front of the bottom bracketmotor and low on the bicycle frame so that the center of mass of thebicycle is low. Further, such a configuration allows the battery to beloaded from the bottom of the bicycle and allows for easy removal.Further, the battery pack and its supports becomes an integral part ofthe structural strength of the frame when secured within the frame.

In another aspect, the second sprocket assembly includes multiple gears,and a shifting mechanism is provided to move the chain between thegears. In this way, the bicycle may be shifted between gears to minimizethe required torque. In turn, less current is required so that the lifeof the battery may be prolonged. Conveniently, a controller may beprovided to control actuation of the shifting mechanism based on therotational wheel speed and the rotational speed of the first sprocketassembly. In this way, the motor may be kept at a maximum speed byshifting the gears. In this manner, the efficiency of the motor ismaximized.

Advantageously, due to the first clutch in the motor, the chain may beshifted between the gears of the second sprocket assembly while thecycle is coasting. This is because the motor is able to turn the frontsprocket assembly while the cycle is coasting (and without turning thepedals). Such a feature is advantageous in that the cycle is able to beplaced in the appropriate gear which corresponds to the current wheelspeed. Further, by the time the rider comes to a stop, the controllerhas placed the chain in the lowest gear so that starting torque andacceleration may be increased. Similarly, when climbing hills, thecontroller may be employed to shift down so that more torque may beprovided to the rear wheel without using excessive current.

Conveniently, the shifting mechanism may comprise a derailleur and acable that is coupled to the derailleur. A stepper motor is provided andhas a lead screw to tension the cable based on signals received from thecontroller. In this way, the cycle may include a standard derailleurwhich in turn is employed to shift the gears when the cable is moved bythe stepper motor upon receipt of signals from the controller.

In yet another aspect, the cycle includes a throttle to control thespeed of the motor. Conveniently, the throttle may comprise apotentiometer that is mounted within a handlebar. The use of an internalpotentiometer is particularly advantageous in that it does not interferewith conventional bicycle shift mechanisms which may optionally beemployed to shift the chain between the gears.

In one particular aspect, a swing arm is pivotally coupled to the frame,and the wheel is attached to the swing arm. A suspension mechanism isalso disposed between the swing arm and the frame. Such a configurationis made possible by including the motor in the bottom bracket so that itdoes not interfere with the rear suspension.

The invention further provides an exemplary method for operating acycle. According to the method, the cycle has a frame and at least onewheel coupled to the frame. A front sprocket assembly is rotatablycoupled to the frame and a rear sprocket assembly is coupled to thewheel. A chain is positioned between the first sprocket assembly and thesecond sprocket assembly. A motor assembly is provided and has a motordriver to turn the first sprocket assembly and a crank arm to turn thefirst sprocket assembly. Such a cycle is operated by actuating the motorand optionally turning the crank arm. The motor is engaged to turn thefirst sprocket assembly if the motor driver is turning faster than thefirst sprocket assembly. However, if the crank arm is rotated fasterthan the first sprocket assembly, the crank arm is engaged with thefirst sprocket assembly. In this way, the rider may choose to have themotor drive the bicycle simply by not turning the crank arm. When therider wishes to operate the bicycle using human leg power, the ridersimply turns the crank arm until the first sprocket assembly is rotatingfaster than the motor driver. Preferably, when the rider begins to turnthe crank arm, such action will not cause the motor to rotate.

In one particular aspect of the method, a second sprocket assemblyincludes multiple gears. In this way, the gears are shifted to maintainthe motor speed at a near maximum output level while the front sprocketassembly rotates at a rate within the range of the human leg. In thisway, the user is able to take over propulsion of the cycle by simplypedaling faster than the motor driver as previously described.Preferably, the motor is operated at a rate in the range from about1,800 rpm to about 3,600 rpm, and the front sprocket assembly is turnedat a rate in the range from about 60 rpm to about 120 rpm.

In one particularly preferable aspect, the gears are shifted withoutturning the crank arm. This is made possible by having the motor turnthe front sprocket assembly without turning the crank arm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an exemplary electric assist bicycleaccording to the invention.

FIG. 1A is a cross sectional view of a frame of the bicycle of FIG. 1taken along lines A—A.

FIG. 1B is a cross sectional view of an alternative frame for holding arectangular battery pack.

FIG. 2 is an exploded perspective view of an exemplary electric motorassembly of the bicycle of FIG. 1.

FIG. 3 is a cross-sectional side view of the motor of FIG. 2.

FIG. 4 is a cross-sectional end view of the motor of FIG. 3 taken alonglines 4—4.

FIG. 5 is a cross-sectional end view of the motor of FIG. 3 taken alonglines 5—5.

FIG. 6 is a cross-sectional side view of a throttle assembly of thebicycle of FIG. 1 according to the invention.

FIG. 6A is an end view of the throttle assembly of FIG. 6.

FIG. 7 is a schematic diagram of an exemplary shifting system accordingto the invention.

FIG. 8 is a schematic view of the electronic circuitry employed in thebicycle of FIG. 1.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The invention provides exemplary electric assisted bicycles as well asmotor assemblies for use with such bicycles. Although describedprimarily in terms of bicycles, it will be appreciated that theprinciples of the invention may be used with any type of cycle. Oneimportant feature of the invention is that it includes a motor/gearreduction assembly that is an integral part of the bicycle bottombracket and is employed to drive the front sprockets directly by use ofa motor driver. By directly driving the front sprockets, the motor maytake full advantage of the large range of mechanical gear reductionscommon to the modern bicycle. Use of such gear reductions allows for theefficiency of the electric motor and battery to be maximized.

The electric motors of the invention are configured to use a minimalamount of current. Because the available energy from the batterydecreases exponentially with current discharge, the motors of theinvention are able to significantly increase the operating time of thebatteries. For example, by utilizing the large range of mechanical gearreductions in the modern bicycle, the required torque to drive thebicycle is kept at a minimum. Since motor torque increases linearly withmotor current, the invention is able to utilize the mechanical gearreductions to keep torque, and hence the required current, as low aspossible.

Configuration of the bicycles of the invention in this manner providesignificant advantages over prior art electric bicycles. For example,bicycles having a motor mounted directly to the rear wheel have only afixed gear ratio. As such, to obtain a four times increase in torque,the motor current must be increased by four times. The motors of thepresent invention utilize the 4.5:1 gear ratios of the modern bicycle toproduce a four times increase in wheel torque with no increase incurrent, and no decrease in efficiency.

Conveniently, the bicycles of the invention may employ the use of acontroller or microprocessor to accomplish automatic shifting. In thisway, the efficiency of the motor is optimized by constantly shifting tothe correct gear to reduce the amount of torque required to drive thebicycle. Further, by utilizing the mechanical gear reductions of themodern bicycle, the motor may be operated near its maximum output level.In this way, the motor is able to operate in its most efficient range tofurther decrease the amount of motor and battery current losses.

Another important feature of the bicycles of the invention is that theyare able to operate using either electric power or human power, therebyincreasing the overall efficiency of the bicycle. One particular featureof the invention is that the motors include a gear reduction assemblythat turns the front sprockets at a rate which is comparable to the rateat which a rider would turn the front sprockets. This configurationprovides a way to easily change between electric power control and humanpower control of the bicycle. Conveniently, the motors of the inventionmay include a clutch mechanism which allows the rider to use human powersimply by pedaling faster than the output of the motor. Conversely, whenthe rider stops pedaling, the motor will be engaged to drive the frontsprockets.

The motors of the invention are preferably configured so that when therider pedals to turn the front sprockets, such pedaling does not turnthe motor. Still another feature of the motors of the invention is thatthe crank spindles are not rotated by the motor, but only by the rider.

One particular advantage of utilizing the mechanical gear reductions ofthe modern bicycle is that such a transmission has been optimized to beextremely efficient. By coupling the motor of the invention with thistransmission, great efficiencies are achieved. Further, the motors ofthe invention are preferably configured so that they are simple in theirdesign to reduce internal frictional losses to further increase theefficiency of the motors. In one exemplary embodiment, both the motorand the gear reduction assembly are concentrically disposed about thecrank spindle so that the resulting motor assembly is both simple in itsdesign and efficient. Further, such a design is compact and lightweightto allow it to easily fit within the bottom bracket of the bicycle.

By utilizing the motors of the present invention with the mechanicalgear reductions of the modern bicycle, other advantages are alsoprovided. For example, the bicycles of the invention are able to provideadequate hill climbing ability and acceleration, while other electricbicycles which utilize a motor in the hub or a friction device whichcouples the motor directly to the tire, have a fixed gear ratio andcannot provide adequate hill climbing ability or acceleration. Moreover,as previously described, the bicycles of the invention are able tominimize torque, and thereby minimize current, when climbing hills andrapidly accelerating.

By employing the electric motors of the invention to directly turn thefront sprockets, the bicycles of the invention may use conventionalderailleurs or shifting mechanisms. This is because the rotating frontsprockets drive the chain as with a conventional bicycle. Conveniently,the controllers or microprocessors of the bicycles may be coupled to anactuator which shifts the gears to optimize the performance of thebicycle.

Another feature of the invention is that it may employ the use of athrottle that does not interfere with shifting mechanisms on the handlebar, such as a Shimano type SIS rapid fire lever. Preferably, thethrottles include a potentiometer or other sensing device that isinternally disposed within the handlebar so that it does not interferewith a conventional shifting mechanism that is coupled to the handlebar. The potentiometers may be actuated by rotating the handle grip orby applying pressure to the grip. As the rider rotates the potentiometeror increases the pressure on the potentiometer, the speed of the bicycleincreases.

Another feature of the bicycles of the invention is that they may beprovided with a monocoque frame which includes a cavity which allows thebatteries to be held directly in front of the bottom bracket while beingdisposed as close to the bottom bracket as possible. In this way, thecenter of gravity in the bicycle is moved to the lowest possible point.In turn, this improves the handling and minimizes the effect of theadditional weight of the battery. Further, the battery pack may besecured to the frame to become an integral structural part of the frame.Another advantage of positioning the battery in the frame and includingthe motor in the bottom bracket is that the motor becomes a part of theswing arm and allows for the use of a rear suspension. The motor mayalso be attached to the frame (in the bottom bracket) to also allow forthe swing arm.

The bicycles of the invention may optionally include a smart controllerto monitor motor current and limit the motor output to provide differentlevels of efficiency and acceleration in response to rider input. Thebicycles may also include a motor controller that allows for highacceleration torque, e.g., up to about 10 times the normal ridingtorque. Excessive heat generation in the motor may be limited by thesmart controller that tapers off the current during a short programmedtime. A thermal sensor may also be mounted in the motor so that thesmart controller may monitor the temperature of the motor and adjust themaximum current to prevent overheating of the motor.

The bicycles of the invention may also employ the use of a torque sensorso that motor torque can be a multiple of the rider torque as requiredby many national laws governing electric bicycles. Further, the motorcontroller may be programmed so that the motor does not begin turninguntil the rider begins turning the pedals at a certain rate ofrevolution. In this way, the efficiency of the battery may be improvedsince human power is required to initially accelerate the bicycle.

In still another feature, the bicycles of the invention may beconfigured to have the motor voltage modulated with a pulse widthmodulation. In this way, the motor maximum voltage is kept below theminimum battery voltage so that the top speed of the bicycle does notdecrease as battery voltage decreases. Preferably, this will be about20% of the maximum battery voltage.

Referring now to FIG. 1, an exemplary embodiment of an electric assistbicycle 10 will be described. Bicycle 10 comprises a frame 12 to which afront wheel 14 and a rear wheel 16 are coupled. Also coupled to frame 12is a handlebar assembly 18 and an adjustable seat 20. As shown, bicycle10 is a mountain-type bicycle and includes a front suspension 22 and arear suspension 24 as is known in the art. However, it will beappreciated that the electric assist features of the invention may beused with essentially any type of bicycle and is not limited tomountain-type bicycles.

Bicycle 10 further includes a swing arm 26 which is pivotally coupled toframe 12. Use of swing arm 26 is advantageous in that suspension 24 maymore effectively be utilized. At the bottom of swing arm 26 is anelectric motor assembly 28. Motor assembly 28 includes one or more gearswhich define a front sprocket assembly 30. Rear wheel 16 includes aplurality of gears defining a second sprocket assembly 31. As is knownin the art, a chain is coupled to the first sprocket assembly and thesecond sprocket assembly so that as the first sprocket assembly isturned, rear wheel 16 will be turned. Further, associated with frontsprocket assembly 30 and rear sprocket assembly 31 are front and rearderailleurs, respectively, for moving the chain between the variousgears of the front sprocket assembly and the rear sprocket assembly asis known in the art. Although not shown, front and rear brakes arepreferably also included as is known in the art to slow or stop thebicycle. Optionally, actuators for actuating the derailleurs and thebrakes may be mounted on handlebar assembly 18.

Coupled to front sprocket assembly 30 are a pair of crank arms 32 towhich a pair of pedals 34 are coupled as is known in the art. In thisway, a rider is able to turn pedals 34 to rotate front sprocket assembly30. This then moves the chain to turn rear sprocket assembly 31 andthereby turn the rear wheel 16.

As described in greater detail hereinafter, bicycle 10 may be placed ina manual mode where wheel 16 is turned only by operation of pedals 34.Alternatively, bicycle 10 may be placed in an automatic mode where motorassembly 28 serves to turn rear wheel 16. Finally, bicycle 10 may beconfigured so that the rider may choose to have motor assembly 28operate the bicycle or the user may choose to manually operate thebicycle simply by turning pedals 34 faster than the motor assembly isable to rotate front sprocket assembly 30.

As shown, frame 12 is of monocoque design and includes a central cavityfor holding a battery pack 36. Battery pack 36 is electrically coupledto motor assembly 28 and provides the necessary power to operate themotor assembly. Various electronics 38, including a controller 38 a anda battery charger 38 b, are also disposed within the central cavity offrame 12 and serve to control the various electrical features of thebicycle as described in greater detail hereinafter. Preferably, frame 12is constructed to have an opening at a bottom end 40 into which batterypack 36 and the electronics 38 are inserted. However, frame 12 may haveother openings to provide access to the battery, including the top endand the sides. Wires 47 extend from battery pack 36 to motor assembly 28so that electrical current may be provided to motor assembly 28.Electronics 38 also includes battery recharger 38 b having a 110 V plug41 which is held by a power cord retraction mechanism 45. In this way,plug 41 is retractable to allow plug 41 to conveniently be plugged intoa conventional power outlet to recharge battery pack 36.

Use of the monocoque design is advantageous in that frame 12 isaesthetically pleasing in appearance. The monocoque design also providessignificant structural stability for bicycle 10. Also, mounting bolts 43are employed to secure battery pack 36 to frame 12 to increase thestructural stability of the bicycle. Further, this design allows batterypack 36 to be placed as low as possible on bicycle 10 so that the centerof gravity of bicycle 10 is also low to further increase the stabilityof bicycle 10. As previously mentioned, use of the monocoque designallows for the use of swing arm 26 to be pivotally coupled to frame 12to improve the suspension of bicycle 10. As still another advantage, themonocoque design provides protection to battery pack 36 from externalimpact blows and from the environment. Still further, the monocoquedesign allows more room for the battery pack because there are not frametubes to interfere with the location of the batteries as withconventional bicycle frames.

Frame 12 is preferably constructed to have an aerodynamic design. Asshown in FIG. 1A, battery pack 36 may conveniently be constructed ofcylindrical batteries (or cells) 37 to facilitates the aerodynamicdesign. Use of cylindrical batteries is also advantageous in thatcooling spaces are provided around the batteries. It will beappreciated, however, that other battery shapes may be used. Forexample, as shown in FIG. 1B, frame 12′ may have a rectangular interiorto hold a rectangular lead acid battery.

Battery pack 36 is preferably constructed of two or more lead acid typebatteries, commercially available from a variety of companies, such asHawker. Such batteries are typically rated at 12 volts each and are ableto deliver 100 amps of current. Such batteries typically weigh about10.8 lbs. each, and are able to operate about one hour betweenrecharges, assuming the bicycle is operating on level ground. However,it will be appreciated that other battery types may be used. Forexample, as previously described in connection with FIG. 1A, cylindricalbatteries, such as NiMH or NiCAD with 1.2 volts/cell and with 30 cells,may also be used. Such a package of 30 cells weighs about 17 lbs.

Bicycle 10 preferably also includes a display panel that is mounted tohandlebar assembly 18. The display panel includes various displays andswitches which are coupled to electronics 38 by a control wire 49 tofacilitate operation of the bicycle 10 as described in greater detailhereinafter.

Referring now to FIGS. 2 and 3, construction motor assembly 28 will bedescribed. Although hidden from view, electric motor assembly 28 isdisposed within a bottom bracket of swing arm 26. In this way, theweight of the motor assembly is disposed as low as possible on bicycle10 to lower its center of gravity. Further, by providing a simpledesign, the motor assembly is able to fit within the bottom bracket,thereby further enhancing the physical appearance of the bicycle.

Motor assembly 28 includes a number of components which are coaxial witha main spindle 42. Further, main spindle 42 is also coaxial with thebottom bracket of the bicycle frame. Main spindle 42 which passesthrough the entire motor assembly, and is supported by left and rightspindle bearings 44 and 46, respectively. (See FIG. 3.) The outsidediameter of left spindle bearing 44 is mounted to a main housing 48.Main housing 48 is employed to house most of the components of the motorassembly and conveniently fits within the bottom bracket of the bicycleas previously described. Right spindle bearing 46 is mounted in anoutput driver 50. Coupled to main spindle 42 is a left crank arm 52 anda right crank arm 54. Crank arms 52 and 54 are coupled to spindle 42with a tapered positive engagement and by the use of screws 56 which arescrewed into threaded slots 58 in main spindle 42.

Motor assembly 28 further includes a motor rotor assembly 60 which ismounted to the outside diameter of rotor ball bearings 62. (See FIG. 3.)A motor magnet 64 is fixed to motor rotor assembly 60. The innerdiameter of rotor ball bearings 62 are mounted on spindle 42. Motorrotor assembly 60 is free to rotate independent of spindle 42 as well ascrank arms 52 and 54 which are mounted to spindle 42. A motor stator 66is fixed to main housing 48. A plurality of motor control wires 68 exitthrough main housing 48. A circuit board 70 (see FIG. 3) having positionsensing devices is mounted to a left side of main housing 48.

A first planet sun gear 72 is mounted directly to the right side ofmotor rotor assembly 60. The outer diameter of first planet sun gear 72is meshed with three first planet gears 74. The three first planet gears74 are mounted on ball bearings 76. The inner diameter of ball bearings76 are mounted to shafts 78. The ends of shaft 78 are mounted to theflange of a second sun gear 80.

The outside diameter of second sun gear 80 is meshed with three secondplanet gears 82. Second sun gear 80 is supported on spindle 42 bybearings 84. The outer diameters of first planet gears 74 and secondplanet gears 82 are meshed with a ring gear 86. Ring gear 86 is machineddirectly into main housing 48. The inner diameters of the second planetgears 82 are mounted to ball bearings 88. (See FIG. 3.) The innerdiameter of ball bearings 88 are mounted to shafts 90. Shafts 90 areattached to a motor output driver ring 92. Motor output driver ring 92is supported by the inner diameter of bearing 94 as also shown in FIG.4. The outer diameter of bearing 94 is mounted to a housing end cap 96.

Although motor assembly 28 is shown with bearings 94, it will beappreciated that bearing 94 may be eliminated. In such a case, motorassembly 28 may be modified so that a bearing surface is providedbetween motor output driver ring 92 and output driver 50 in a mannersimilar to that described in U.S. Pat. No. 5,570,752, the disclosure ofwhich is herein incorporated by reference.

Output driver 50 is supported by bearings 98. The outer diameter ofbearings 98 are mounted in housing end cap 96. Mounted in the right endof output driver 50 is a crank driver ring 100. Mounted in right crankarm 54 are crank ratchet pawls 102, as also shown in FIG. 5. Ratchetpawls 102 are employed to engage crank driver ring 100 as described ingreater detail hereinafter.

Mounted in the left outside diameter of output driver 50 are a pluralityof driver ratchet pawls 104 which are employed to engage motor outputwith driver ring 92 as described in greater detail hereinafter. Theright outside diameter of output driver 50 is attached to a sprocketsupport 106. Sprocket support 106 is attached to front drive sprockets108.

Electric motor assembly 28 is advantageous in that it allows bicycle 10to be operated in three modes. The first mode is pedal only power. Thesecond mode is motor only power, and the third mode is a variablecombination of both pedal and motor power. For pedal only power,pedalling of crank arms 52 and 54 by the rider causes the frontsprockets 108 to rotate without rotating motor rotor assembly 60. Inthis way, significant friction losses to riding the bicycle areeliminated.

When crank arms 52 and 54 are rotated by the rider, spindle 42 rotatesfreely in bearings 44 and 46. Motor rotor assembly 60 does not rotatedue to bearings 62. Further, second sun gears 80 do not rotate becauseof bearings 84. The rotation of crank arm 54 causes crank ratchet pawls102 to engage crank driver ring 100. This causes output driver 50 torotate. Sprocket support 106 and sprockets 108 rotate with output driver50. The rotational speed of sprockets 108 and crank arms 52 and 54 arethe same.

The rotation of output driver 50 does not cause motor output driver ring92 to rotate because driver ratchet pawls 104 do not engage motor outputdriver ring 92 in this direction. Because the output driver 50 is notengaged with motor output driver ring 92, there is no drag on crank arms52 and 54 due to motor friction and the bike pedals rotate freely as ona normal non-motorized bicycle.

For motor only power, the motor drives sprockets 108 but not the crankarms 52 and 54 which may otherwise cause injury to the rider. Therotation speed of sprockets 108 is reduced from the speed of motor rotorassembly 60 by the combined ratio of the two planet gear sets.

When motor power only is used, a magnetic field in motor stator 66causes motor rotor assembly 60 to rotate. First sun gear 72 rotates withmotor rotor assembly 16. The rotation of first sun gear 72 causes thefirst planet gears 74 to rotate. Due to the fixed nature of ring gear 86and the relationship of the planetary gears, the speed of the second sungear 80 is reduced by the design ratio. Preferably, the ratio isapproximately 5.6 to 1. However, it will be appreciated that otherratios may also be employed. Rotation of second sun gear 80 causes thethree second planet gears 82 to rotate in ring gear 86. This secondrotation causes another reduction. Preferably, this reduction is also5.6 to 1. However, other reductions may also be employed. Due to themultiplication of gear trains, the overall speed reduction of the motoroutput driver ring 92 is 31.86 to 1. In other words, the speed of motoroutput driver ring 92 is reduced to 31.86 times from the speed of motorrotor assembly 60.

As motor output driver ring 92 rotates, it engages motor driver ratchetpawls 104 and causes output driver 50 to rotate. As with pedal-onlypower, the rotation of output driver 50 causes sprockets 108 to rotate.The rotation of output driver 50 does not cause crank arms 52 and 54 orspindle 42 to rotate because crank ratchet pawls 102 do not engage crankdriver ring 100 in this direction.

In the mode having a variable combination of pedal and motor power,power is delivered either by the motor or the rider. If the motor speedis higher than the pedal speed, the motor will cause the bicycle to gofaster. However, if the rider increases pedaling speed above the motorspeed, the rider will make the bicycle move. Hence, the engagement ofoutput driver 50 depends on the relative speed of the motor and pedals.Whichever is rotated faster will drive the sprockets 108.

The invention further provides the ability to recharge the batteries byturning of the pedals. In this option, the motor clutch (motor driverratchet pawls 104) may be eliminated and direct contact made betweenmotor output driver ring 92 and output driver 50. In this manner, whenthe pedals rotate, the motor also rotates. To eliminate the drag fromthe motor in pedal only mode, the motor turns just enough to eliminatethe drag.

EXAMPLE

The electric bicycle of FIG. 1 was theoretically compared to aconventional direct drive electric bike. The electric assist bicycle ofthe invention was provided with multiple gears. Both bicycles weretested for two situations. First, travel was on level ground at 20 mph.In the second situation, hill climbing was performed at 5 mph.Controller losses are not included in this example and are assumed to bethe same for both cases.

The results of the test are illustrated in Tables 1 and 2 below.

TABLE 1 Comparison at 20 MPH on Flat Ground with 66 in-LB Wheel TorqueDirect Drive to Bottom Bracket Motor Wheel 8:1 Fixed (Multiple GearRatios) 4:1 Motor Reduction Final Gear Reduction Motor Resistance 0.1ohm 0.1 ohm Torque Constant 11 in oz/amp 11 in oz/amp Voltage Constant 8volts/KRPM 8 volts/KRPM Battery System 24 VDC 24 VDC Voltage MotorTerminal 20.4 Volts 20.4 Volts Voltage (1) Motor Current 12 Amps 12 AmpsInput Power 245 Watts 245 Watts Output Power 231 Watts 231 WattsResistive Losses 14 Watts 14 Watts Motor Efficiency 94% 94% Motor Speed2400 RPM 2400 RPM Wheel Speed 300 RPM (20 MPH) 300 RPM (20 MPH) WheelTorque 66 in-LB 66 in-LB Battery Rating 12 amp-hr 12 amp-hr BatteryCurrent (1) 10.2 Amps 10.2 Amps Battery Run Time (2) 50 minutes 50minutes Battery Energy 204 watt-hr 204 watt-hr (1) Based on PWM controlof motor speed. (2) Based on Published Current Vs Run Time Data

TABLE 2 Comparison at 5 MPH Hill CLimbing with 264 in-LB Wheel TorqueDirect Drive to Bottom Bracket Motor Wheel 8:1 Fixed (Multiple GearRatios) 1:1 Motor Reduction Final Gear Reduction Motor Resistance 0.1ohm 0.1 ohm Torque Constant 11 in oz/amp 11 in oz/amp Voltage Constant 8volts/KRPM 8 volts/KRPM Battery System 24 VDC 24 VDC Voltage MotorTerminal 10 Volts 10 Volts Voltage (1) Motor Current 48 Amps 12 AmpsInput Power 480 Watts 245 Watts Output Power 250 Watts 231 WattsResistive Losses 230 Watts 14 Watts Motor Efficiency 52% 94% Motor Speed600 RPM 2400 RPM Wheel Speed 750 RPM (5 MPH) 75 RPM (5 MPH) Wheel Torque264 in-LB 264 in-LB Battery Rating 12 amp-hr 12 amp-hr Battery Current(1) 20 Amps 10.2 Amps Battery Run Time (2) 20 minutes 50 minutes BatteryEnergy 158 watt-hr 204 watt-hr (1) Based on PWM control of motor speed.(2) Based on Published Current Vs Run Time Data

This example illustrates that on level ground, the motor efficiency ofboth systems is approximately the same, i.e., about 94%. Battery runtime is 50 minutes. However, with hill climbing efficiency changesradically. For the bicycle of FIG. 1, utilization of the 4:1 gear changereduction, maintains the motor efficiency at 94% with a battery run timeof 50 minutes. In comparison, the direct drive bicycle motor efficiencydropped by almost one half to 52%. Further, the battery run time wasreduced to almost a third and was only about 20 minutes. In both cases,power output to the rear wheel is kept constant at 231 watts.

Acceleration of electric motor assembly 28 is preferably accomplished byuse of a throttle assembly 110 as illustrated in FIG. 6. Conveniently,throttle assembly 110 is coupled to handlebar assembly 18. Throttleassembly 110 comprises a rubber grip 112 which is disposed about athrottle sleeve 114. Coupled to throttle sleeve 114 is a planet gear 116which revolves around a sun gear 118. Throttle assembly 110 furtherincludes a potentiometer 120 which is rotated when grip 112 is rotated.The potentiometer then sends a signal through wires 122 which arecoupled to electronics 38 (see FIG. 1) so that electrical current can besupplied to motor assembly 28.

Conveniently, a spring 124 is provided to bias grip 112 in a homeposition so that when released, grip 112 will return to the homeposition and no electrical current will be supplied to motor assembly28. An end cap 126 provides a convenient covering for the internalcomponents. Use of throttle assembly 110 is particularly advantageous inthat it has a low profile on handlebar assembly 18 so that othercomponents may be placed on handlebar assembly 18 without interferencefrom throttle assembly 110.

The invention further provides an exemplary shift system that allows forautomatic shifting on the bicycles of the invention as well as for anystandard bicycle. The shift system of the invention allows for automaticshifting on essentially any type of gear system including those havingconventional derailleurs, those having internal hub systems, and thelike. The shift system of the invention is particularly useful with thebicycles described herein because such bicycles are able to turn thefront sprockets without turning the pedals. In this way, the shiftsystem of the invention is able to take advantage of the turningsprockets to constantly shift to the correct or desired gear, even whencoasting to a stop when the rider is not pedaling.

By automatically shifting to the correct gear, the shift system enablesthe bicycle to be operated at an optimal torque level. With the electricbicycles of the invention, this is advantageous because minimal currentis required since torque is optimized. By way of example, one of theproblems associated with both regular bicycles and electric bicycles isthe need to shift to a lower gear when coasting to a stop sign.Otherwise, the bicycle will be in a high gear when exiting the stopsign, making it difficult to turn the pedals or to operate the motor. Aconventional derailleur system requires the chain to be moving forshifting to occur. Because the motor of the invention is able to rotatethe front sprockets without rotating the pedals, the bicycle can beshifted while coasting to a stop. Further, the shift system of theinvention takes advantage of the moving chain to automatically shift thebicycle to the correct gear depending upon the wheel speed. With theelectric bicycle, automatically shifting is further important becausethe electric bicycle accelerates much faster than a conventionalbicycle, requiring the rapid shifting of the gears.

To optimize efficiency, the electric motors of the invention arepreferably kept at maximum speed (which preferably equates to a pedalspeed of about 75 rpm). By operating the motor at a maximum rpm,internal heat losses are minimized. Hence, by knowing the gear ratiosand the wheel speed, the shift system employs the use of amicroprocessor to shift to the correct gear for the current speed. Inthis way, when the motor is running, the motor speed is kept at amaximum so that motor efficiency is optimized. If the rider addsadditional power through the pedals, the microprocessor is configured toshift to a higher gear. Such variables are preferably programmed intothe microprocessor to optimize the efficiency for each rider.

Referring to FIG. 7, an exemplary embodiment of a shift system 130 willbe described. Shift system 130 includes a linear stepper motor 132 tomove a derailleur cable 134. An exemplary stepper motor that may be usedis a Haydon Switch and Instrument stepper motor, part no. 46441-12.Cable 134 is coupled to a derailleur shifting mechanism 136 or aninternal hub shifting mechanism as is known in the art. Conveniently, acable adjuster 138 may be provided to adjust the tension in cable 134.Stepper motor 132 is electrically coupled to a controller 140 ormicroprocessor. The amount of movement of stepper motor 132 is basedupon the specific type of shifting mechanism and is programmed intocontroller 140. The drive for stepper motor 132 is a conventionalstepper motor drive as is known in the art. As an alternative to using astepper or DC motor to move cable 134, it will be appreciated that otherdesigns may be employed including use of a rotating motor with a gearreduction. Stepper motor 132 further includes a limit switch 142 whichis used to define a home position on power up of stepper motor 132.Limit switch 142 may be a contact type or non-contact type of switch.

In operation, stepper motor 132 is given a number of pulses bycontroller 140 to cause the motor to move an exact amount. It will beappreciated that various position sensors may also be employed todetermine the position of stepper motor 132.

Also coupled to the controller is a wheel speed sensor 144, a frontsprocket speed sensor 146, and a handle bar interface 148. With thisconfiguration, controller 140 determines the correct gear by measuringwheel speed with wheel speed sensor 144 and the front sprocket speedwith front sprocket speed sensor 146. Based on the programmed gearratios, controller 140 selects the correct gear and commands steppermotor 132 to move to the required position. Stepper motor 132 then movescable 134 causing derailleur shifting mechanism 136 to shift gears.Because motor 132 moves cable 134, a variety of gear shift mechanismsmay be employed, including both internal hub or derailleur type shiftingmechanisms. Further, it will be appreciated that system 130 may beemployed to shift gears on both the front sprockets and the rearsprockets of the bicycle. Still further, because the electric bicyclesof the invention are able to move the chain, even when the rider iscoasting, the shift system 130 may be employed to place the bicycle in alow gear when the rider coasts to a lower speed or stops altogether sothat the required torque is minimized when the rider begins toaccelerate.

Shift system 130 may be incorporated into bicycle 10 by including thecontroller in the electronic circuitry stored within frame 12 and byincluding the stepper motor and appropriate sensors on the bicycle. Inthis way, bicycle 10 may be operated by using the automatic shiftingfeatures of shift system 130. Conveniently, bicycle 10 may be providedwith a standard shifting system, such as a Shimano-type gear shifter, asis known in the art.

Referring now to FIG. 8, the electrical circuitry of bicycle 10 will bedescribed. The circuitry includes a main board controller 150, a handlebar interface board 152 and a battery charger board 154. Main controllerboard is representative of circuitry 38 of FIG. 1. The voltage of thesystem is preferably 24 volts DC but may optionally be 36 or 48 voltsDC. Main controller board 150 is coupled to a motor 156 which isrepresentative of motor assembly 28 of FIG. 1. Main controller board 150is also coupled to a throttle controller 158 which is representative ofthrottle assembly 110 of FIG. 6. A headlight highbeam 160 and aheadlight lowbeam 162 are also coupled to main controller board 150 sothat the bicycle may be provided with lights. Similarly, a tail light164 is also coupled to main controller board 150. A rear shift steppermotor 166 is coupled to main controller board 150 and is representativeof stepper motor 132 of FIG. 7. Optionally, a front shift stepper motor168 may also be coupled to main controller board 150 to control shiftingof the chain on the front gears.

A battery 170 is further coupled to main controller board 150 and isrepresentative of battery pack 36 of FIG. 1. Charger board 154 is alsocoupled to battery 170. Charger board 154 is configured so that it maybe coupled to a power supply 172, which for convenience of illustrationis shown as a 110 VAC, 15 amp power supply. However, it will beappreciated that other power supplies may be used. Charger board 154preferably includes a retractable cord which will allow it to be coupledto power supply 172. Charger board 154 is configured to sense thevoltage of battery 170 and will automatically configure itself for sucha voltage. Charger board 154 may alternatively be configured to monitorboth the temperature and voltage of battery 170. Further, charger board154 may charge using either a constant voltage or constant current.Charger board 154 is preferably cooled through a heat sink that ismounted to the frame of the bicycle. A fan may also be used for forcedair cooling, if required.

Also coupled to main controller board 150 is a right turn signal 174 anda left turn signal 176. A system enable 178 and a cadence 180 arecoupled to main controller board 150. System enable is a safety-typeinterlock which prevents operation of the bicycle until actuated.Cadence 180 displays the front sprocket speed. A speed sensor 182 and atorque sensor 184 are also coupled to main controller board 150. Speedsensor 182 may be employed to facilitate automatic shifting aspreviously described. Torque sensor 184 may be employed to monitor thetorque of the motor so that shifting may occur using the shift system aspreviously described to keep torque at a minimum.

Handlebar interface board 152 includes an LCD display 186 and a keypad188. Keypad 188 may be employed to control various functions, such ascontrol of headlights 160 and 162. LCD display 186 may be configured todisplay various operating parameters such as bicycle speed, currentgear, battery life, and the like. An LED power use array 190 is includedon handle interface board 152 and is employed to show the amount ofcurrent used. The LED array may also be used to show the amount ofenergy remaining in the battery pack.

The handlebar interface board 152 may optionally include an auto/manualshift pushbutton interface 192 which is preferably located near the lefthand grip of the handlebar. Auto/manual shift 192 is preferablyconfigured to be placed in one of three modes. The first mode is an autoshift mode where shifting is automatic based on wheel speed aspreviously described. The second mode is manual shift where the rider isresponsible for shifting the gear using a conventional shiftingmechanism or keypad 188. The third mode is a manual upshift only, wheredownshifting is automatic, while the rider has the option to shift upwhen they desire. In the automatic shift mode, the gear ratios arepreviously programmed into main controller board 150. The gears arecontinuously shifted to keep the front sprocket at the preprogrammedRPM. When coasting, the motor 156 turns the front sprocket when shiftingso that the derailleur can shift the gears as previously described.

A safety interlock 194 is coupled to handlebar interface board 152 andprevents operation of the bicycle until appropriate password informationhas been entered. For example, safety interlock 194 may require theentry of a numeric key code to activate the bicycle. If tampered with, ahorn may be activated. Safety interlock 194 may also include an on/offswitch to allow for the bicycle to automatically be turned to the manualmode. Further, safety interlock 194 may be configured to set to a“sleep” mode when not in use for a specified time period, such as for 5or more minutes.

A horn, turn signal, high/low beam switch 196 is also coupled tohandlebar interface board 152 and allows for operation of the horn, theturn signals, and the headlights. These switches may also be on aseparate board located hear the rider's left hand for ease of operation.

The invention has now been described in detail for purposes of clarityand understanding. However, it will be appreciated that certain changesand modifications may be practiced within the scope of the appendedclaims.

What is claimed is:
 1. An electric motor assembly, comprising: ahousing; a spindle disposed to rotate in the housing; a motor comprisinga stator coupled to the housing, and a rotor rotatably disposed withinthe stator such that the rotor is disposed about the spindle; an outputdriver; a gear system operably coupled to the rotor and the outputdriver to rotate the output driver upon operation of the motor; and asprocket assembly operably coupled to the output driver such that thesprocket assembly rotates upon rotation of the output driver; whereinthe gear system is coupled to a motor driver, and further comprising afirst clutch to engage the motor driver with the output driver when themotor driver is rotating faster than the output driver, a crank armcoupled to the spindle, and a second clutch to engage the crank arm withthe output driver when the crank arm is rotated faster than the outputdriver, and wherein the first clutch and the second clutch are coaxiallyaligned with an axis of the spindle.
 2. A motor assembly as in claim 1,wherein the housing has a central axis, wherein the spindle is alignedwith the central axis, wherein the rotor is concentrically disposedabout the spindle, and the stator is concentrically disposed about therotor.
 3. A motor assembly as in claim 1, wherein the gear systemcomprises a set of planetary gears to rotate the output driver at a rateof rotation that is less than the motor.
 4. A motor assembly as in claim2, wherein the rate of rotation of the motor is in the range from about1,800 rpm to about 3,600 rpm, and the rate of rotation of the outputdriver is in the range from about 60 rpm to about 120 rpm.
 5. A motorassembly as in claim 1, wherein the motor comprises a brushless DCmotor.
 6. A motor assembly as in claim 1, further comprising at leastone bearing assembly coupled to the housing and disposed about spindleso as to generally prevent rotation of the spindle by the motor uponoperation of the motor.
 7. A motor assembly as in claim 1, furthercomprising a bearing assembly disposed between the rotor and the spindleto generally prevent rotation of the rotor upon rotation of the spindleby the crank arm.
 8. An electric motor assembly, comprising: a housing;a spindle disposed to rotate in the housing; a motor comprising a statorcoupled to the housing, and a rotor rotatably disposed within the statorsuch that the rotor is disposed about the spindle; a crank arm coupledto the spindle; an output driver; and a gear system operably coupled tothe rotor and the output driver to rotate the output driver uponoperation of the motor; wherein the gear system is coupled to a motordriver, and further comprising a first clutch to engage the motor driverwith the output driver when the motor driver is rotating faster than theoutput driver, and a second clutch to engage the crank arm with theoutput driver when the crank arm is rotated faster than the outputdriver, and wherein the first clutch and the second clutch are coaxiallyaligned with an axis of the spindle.
 9. A motor assembly as in claim 8,wherein the housing has a central axis, wherein the spindle is alignedwith the central axis, wherein the rotor is concentrically disposedabout the spindle, and the stator is concentrically disposed about therotor.
 10. A motor assembly as in claim 8, further comprising a sprocketassembly operably coupled to the output driver such that the sprocketassembly rotates upon rotation of the output driver.
 11. A motorassembly-as in claim 8, wherein the gear system comprises a set ofplanetary gears to rotate the output driver at a rate of rotation thatis less than the motor.
 12. A motor assembly as in claim 11, wherein therate of rotation of the motor is in the range from about 1,800 rpm toabout 3,600 rpm, and the rate of rotation of the output driver is in therange from about 60 rpm to about 120 rpm.
 13. A motor assembly as inclaim 8, wherein the motor comprises a brushless DC motor.
 14. A motorassembly as in claim 8, further comprising at least one bearing assemblycoupled to the housing and disposed about spindle so as to generallyprevent rotation of the spindle by the motor upon operation of themotor.
 15. A motor assembly as in claim 8, further comprising a bearingassembly disposed between the rotor and the spindle to generally preventrotation of the rotor upon rotation of the spindle by the crank arm. 16.An electric motor assembly, comprising: a housing; a spindle disposed torotate in the housing; a motor comprising a stator coupled to thehousing, and a rotor rotatably disposed within the stator such that therotor is disposed about the spindle; an output driver; a gear systemoperably coupled to the rotor and the output driver to rotate the outputdriver upon operation of the motor; a crank arm coupled to the spindle;and a clutch disposed in the crank arm to engage the crank arm withoutput driver when the crank arm is rotated faster than the outputdriver.
 17. An electric motor assembly, comprising: a housing; a spindledisposed to rotate in the housing; a motor comprising a stator coupledto the housing, and a rotor rotatably disposed within the stator suchthat the rotor is disposed about the spindle; a set of bearings disposedbetween the rotor and the spindle to permit the rotor to roll over thebearings when rotating about the spindle; an output driver; a gearsystem operably coupled to the rotor and the output driver to rotate theoutput driver upon operation of the motor.
 18. An electric motorassembly, comprising: a housing; a spindle disposed to rotate in thehousing; a crank arm coupled to the spindle; a motor comprising a statorcoupled to the housing, and a rotor rotatably disposed within the statorsuch that the rotor is disposed about the spindle; an output driver; afirst clutch to permit the rotor to rotate the output driver when thefirst clutch is engaged; a second clutch to permit the crank arm torotate the output driver when the second clutch is engaged; wherein theoutput driver includes engaging components of both the first and secondclutch.